Cabletron Systems STS16-20R - Manual (Page 35)

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Switch Overview SmartStack STS16-20D/STS16-20R Token Ring Switches Installation and User Guide
Multiple Bridging Modes
The SmartStack STS16-20D/STS16-20R supports four different switching modes
to provide maximum flexibility in all installation environments. The switching
modes are source route switching (SRS), source route bridging (SRB), source
route transparent
(SRT) and SRT/SRB. The switch operates on two levels (BRF
and CRF) as outlined in the following:
Figure 6. Typical Configuration with SmartStack STS16-20R
Switches Using Multiple Bridging Modes
The switch bridging modes are founded on the concept of logical rings (LR) or
logical segments
in Ethernet. The logical ring is represented on the switch by the
DTR (IEEE 802.5r) standard’s concentrator relay function (CRF). A logical ring
may consist of interconnected CRFs on different switches.
Each port on the switch belongs to a CRF, which is a logical grouping of ports
within the switch. A CRF can consist of any number of ports within a switch or a
switch stack. The ports within a CRF do not have to be adjacent.
The logical rings and subsequently, the CRFs, are assigned a unique ring number
each when the switch performs source routing functions. The bridging is performed
through the logical entity of the bridge relay function (BRF).
CRF 2 CRF 1 CRF 3 CRF 4
BRF 1
Switch